The major goals of this proposed research are to elucidate: 1) the mechanism of action of luteinizing hormone (LH) and human chorionic gonadotropin (hCG) on steroidogenesis in the corpus luteum; and 2) the mechanism of the effects of putative luteolytic agents. These studies will be carried out using bovine and human corpora lutea in vitro. The approach to the first goal is to investigate how LH and cyclic AMP accelerate the rate-limiting step in steroidogenesis, namely the conversion of cholesterol into pregnenolone. This will involve studies on: 1) the cholesterol side-chain cleavage enzyme system; 2) the cholesterol transport into mitochondria and within mitochondria; 3) the cholesterol ester hydrolase enzyme; and 4) the secretion of progesterone. An investigation of the mechanism of action of LH on adenylate cyclase will also be carried out. The approach to the second goal will involve testing substances such as estrogens, prostaglandins and arachidonic acid on incubating isolated luteal cells. If inhibitory effects are demonstrated, their site of action on the steroidogenic pathway and their mechanism of action will be investigated.